1. Field of the Invention
The present invention relates to a gas turbine interstage portion seal device.
2. Description of the Prior Art
A gas turbine stationary blade inner side interstage portion seal in the prior art is carried out, as shown in FIG. 2, with a labyrinth seal fin 52 provided to a stationary side (that is, a stationary blade inner ring 51) and a step seal 54 provided to a rotary side (that is, a turbine disc seal arm portion 53).
In the gas turbine interstage portion seal system using the labyrinth seal fin 52 and step seal 54, while fluid passes through the labyrinth (throttle) portion, it flows through narrow gaps and wider gaps in turn to be pressure-reduced by the throttle effect, and generally in a rotating shaft of rotary machine, this seal system is used when the fluid for sealing is a compressible gas or steam.
It is to be noted that the labyrinth seal 52 exhibits by nature its effect while the rotary machine is in operation and its sealing ability is not necessarily good in a state out of operation.
In order to minimize gas turbine interstage portion gas leakage, the stage number of the labyrinth seal fin 52 may be increased or the gap between the stationary side and the rotating shaft may be reduced. But if the stage number is increased, it leads to elongation of the rotating shaft, resulting in a problem in the strength of the rotating shaft. If the gap is too small, the rotating shaft will come in contact with the stationary side due to thermal expansion when there is run-out of the rotating shaft.
Therefore, the seal fin 52 is made of a soft material and is worked to form a sharp edge at its end in consideration that if contact occurs, the seal fin 52 wears quickly so that the rotating shaft may not be damaged.
The prior art gas turbine interstage portion seal, as mentioned above, is carried out with the labyrinth seal fin provided on the stationary side and the step seal provided on the rotary side.
In the case of this seal system, considering quickness of thermal expansion on the rotary side when the temperature of the stationary side is low at start-up time, it is necessary to make the gap wider in advance to avoid contact of both these sides. If the gap between both sides is made wider, however, it will cause a lowering of the sealing ability in the regular operation, resulting in increase of loss of leakage, and an this is one of the factors to lower the gas turbine performance.